1. Field
An annular light guide is provided. The annular light guide is disposed in the back of a face plate or the like of rotary operation type electrical components. The electrical components have an illumination area along the circumferential direction and is used for illuminating the illumination area while guiding light from a light source.
2. Related Art
Conventionally, rotary operation type electrical components e are used in in-car air conditioner systems, in-car audio systems and the like. These systems use an illumination system adopted so that rotational position of a rotary knob is rotated by a passenger and is visible even in a dark place. In the illumination system, an annular thin face plate with an indicator is provided along the circumferential direction and is disposed around a rotary knob. In the back of the face plate there is an annular light guide. In this configuration, light from a light source such as a lamp illuminates the indicator of the face plate through the annular light guide (e.g., see JP-A-2004-227855).
FIG. 5 is a sectional view showing a conventional illumination system applied on a rotary operation type electrical component. FIG. 6 is a plan view showing the illumination system. A rotary operation type electrical component 1 shown in FIGS. 5 and 6 is provided with the following: a rotary knob 2 which is rotated by a passenger, a rotary encoder (here, only the rotary shaft 6 is shown) which is rotationally driven in conjunction with the rotary knob, an annular thin face plate 3 disposed around the rotary knob 2, a holder 4 which secures the inner circumferential region and the outer circumferential region on the back surface of the face plate 3 by bonding, an annular light guide 5 held by the holder 4, a light source 7 such as lamp which is disposed adjacent to one side surface 5c of the annular light guide 5, and a circuit board 8 mounted with the above-mentioned rotary encoder, light source 7 and others. The face plate 3 is provided with an indicator 3a which is supposed to be an illumination area and is located along the circumferential direction. The annular light guide 5 faces the back of the indicator 3a of the face plate 3.
The annular light guide 5 is a molded product made of highly optically transparent material such as acrylic resin, and is formed such that a small diameter inner ring portion 5a and a large diameter outer ring portion 5b are connected to appropriate points in the annular light guide. The annular light guide 5 guides light, which is emitted from the light source 7 and is incident to a side surface 5c, to each of the ring portions 5a and 5b and then makes the light emit forward.
The light guide 5 has a structure such that illumination light emitted from the front of the inner ring portion 5a illuminates a position mark 2a of the rotary knob 2, and illumination light emitted from the front of the outer ring portion 5b illuminates the indicator 3a of the face plate 3. Meanwhile, another annular light guide is known which is formed in a wide toric shape without a clearance between the inner ring portion 5a and the outer ring portion 5b. 
The illumination area of the rotary knob 2 is only where the position mark 2a is. Also, a flange portion 2b protrudes from the rotary knob 2 and prevents light from leaking during illumination. The face plate 3 is formed in such a manner that light-blocking coating is applied to the front surface of an optically transparent resin plate, and on the whole back surface of the resin plate there is pasted a colored, toned sheet, whereby the indicator 3a is illuminated by the annular light guide 5 with a desired color corresponding to the toned sheet.
The indicator 3a is an illumination area in which figures, letters or the like for indicating a rotary position of the rotary knob 2 are displayed along the circumferential direction. Thereby, a passenger can visually recognize the rotational position of the rotary knob 2 by visually observing what part of the indicator 3 is pointed at by the position mark 2a. The holder 4 is a resin molded product, and also serves as an upper case to be integrated with a lower case (not shown). Each of the front surfaces of a smaller diameter annular ring 4a and a larger diameter annular ring 4b of the holder 4 fixes the face plate 3 by bonding. The circuit board 8 is provided in the above-mentioned lower case. The rotary operation type electrical component 1 is constructed to be electrically connected to an external circuit by way of the circuit board 8 and a connecter unit (not shown) provided in the lower case.
The rotary operation type electrical component 1 thus constructed is embedded in a round opening 11 formed in a front panel 10 in a car interior in such a state that the indicator 3a of the face plate 3 and the rotary knob 2 are exposed, and is set such that the rotary knob 2 protrudes forward from the opening 11. When a passenger rotates the rotary knob 2, he can check the rotational position by visually observing the relative position between the position mark 2a and the indicator 3a. Moreover, even in a dark place at night or the like, the position mark 2a and the indicator 3a can be viewed at ease due to illumination light emitted from the back side, so that a passenger has no difficulty in rotating the rotary knob 2.
Japanese Patent Application Publication No. 2004-227855 (page 2-3, FIG. 6) is an example of related art.
The conventional known annular light guide 5 described above is one that makes light from the light source 7 such as lamp enter the one side surface 5c and then guides the light to a forward illumination area (the position mark 2a and the indicator 3a). Therefore, light from the light source 7 which is not incident to the side surface 5c can not be utilized, so that there has been a problem that illumination efficiency is poor. In other words, since light from the light source 7 is emitted in all directions, light which derives from the light source 7 and is emitted in directions where the annular light guide 5 is not present (e.g., light emitted in the right direction in FIG. 5) all diffuses in vain. Further, all light incident on the one side surface 5c of the annular light guide 5 can not be utilized as illumination light, and light leaks from the annular light guide 5, that is, some light is emitted from the external wall and the like of the annular light guide 5 in undesired directions. As the result, only part of light from the light source 7 can be used as illumination light for the illumination area, thus causing a lack of brightness and higher power consumption of the light source 7.